Metal organic chemical vapor deposition apparatus and deposition method

ABSTRACT

A metal organic chemical vapor deposition apparatus comprising a source ampule, a liquid micro-pump, a vaporizer equipped with a solvent supply means, and a reactor. A reactant dissolved in a solvent in the source ampule is transferred to the vaporizer by the liquid micro-pump. A sufficient amount of the solvent is additionally fed to the vaporizer by the solvent supply means, concurrently with the transfer, and vaporized along with the reactants. After being vaporized in the vaporizer, the reactant is injected to the reactor by carrier gas and deposited on a semiconductor substrate to form a high dielectric thin film. By virtue of the additional supplied solvent, the recondensation of the reactant in the vaporizer, which is attributed to the separation of the solvent from the reactant, can be prevented in the vaporizer and in the transfer line between the vaporizer and the reactor. In addition, the residues of the reactant, which may result from the separation, can be washed off by providing the solvent through the supply means to the vaporizer.

This application is a division of U.S. application Ser. No. 08/921,560,filed Sep. 2, 1997, now U.S. Pat. No. 6,008,143, issued Dec. 28, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a metal organic chemical vapordeposition (hereinafter referred to as “MOCVD”) apparatus and to adeposition method. More particularly, the present invention relates toan MOCVD apparatus useful to deposit high dielectric thin film on asemiconductor substrate and to a deposition method using the same.

2. Description of the Prior Art

For the next generation DRAMs which are at least 1 Giga in memory size,conventional thin films not supply enough capacitance. As semiconductordevices scale down, three-dimensional capacitor structures, such as finand cylinder type structures, are more difficult to construct becausethe scaling-down is accomplished at the sacrifice of cell areareduction.

In addition, reduction in the thickness of the thin film gives rise toan increase in leakage current at a source/drain region, an impurityregion of a semiconductor device, and causes a soft error, a phenomenonwherein the information stored in a capacitor is changed or lost byα-particles. So, a reliable capacitor is difficult to obtain. Further,if a capacitor is formed into a complex three-dimensional structure,subsequent processes are hard to perform.

Recently, active research has been directed to a high dielectric thinfilm deposition apparatus in order to apply high dielectric materials,such as BST (BaSrTiO₃) and SrTiO₃, for the thin film of a capacitor.

To construct high dielectric thin films, many methods are used,including a sputtering method, a sol-gel method, a laser ablationmethod, an MOCVD method, etc. Of them the MOCVD method guarantees auniform thin film as well as allows the composition of the thin film tobe easily controlled. Accordingly, the high dielectric thin filmdeposition apparatuses which utilize the MOCVD method are now beingactively researched.

In order to better understand the background of the invention, adescription will be given of a conventional MOCVD apparatus and itsoperation procedure, in conjugation with FIG. 1.

As shown in FIG. 1, a typical MOCVD apparatus comprises a reactantsource ampule 10, a liquid micro pump 20 for delivering the reactants, avaporizer 30, a reactor 70, a trap 60 and a vacuum pump. The reactantscontained in the source ampule 10 are dissolved in a solvent. The liquidmicro-pump 20 is used to transfer the resulting liquid to the vaporizer30 in which the liquid is heated or vaporized with the aid of anotherenergy source. Using a carrier gas, such as argon or nitrogen, the vaporis transferred the rector 70 and the vapor is deposited on asemiconductor substrate loaded in the reactor 70, to form a thin film.Here, pressure rising gas which is needed for the transfer of thereactants, is also argon or nitrogen.

During the transfer of the reactants dissolved in the solvent to thereactor, however, since the vaporization temperature of the solvent ismuch lower than that of the reactants, the solvent, although no heat isapplied to the vaporizer, is separated faster than the reactants,recondensing the reactants. Accordingly, the recondensed reactants blockthe thin film transfer line between the vaporizer and the reactor andthus, are not constantly fed to the reactor. As a consequence, adeposited thin film is formed poor in properties.

Even when heat is applied to the vaporizer in order to constantlymaintain the vapor pressure of the reactants necessary for the thin filmdeposition, the solvent is faster vaporized than the reactants,resulting in the decomposition of the reactants. Likely, the reactantscannot be constantly fed to the reactor since the decomposed reactantsblock the thin film transfer line between the vaporizer and the reactor.So, it is difficult to form a thin film reliable and excellent inelectrical properties.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to overcome theabove problems encountered in the prior arts and to provide an MOCVDapparatus in which the reactants are prevented from being recondensedand decomposed in the vaporizer.

It is another object of the present invention to provide a method forforming a high dielectric thin film by using the apparatus.

In accordance with an aspect of the present invention, there is providedan MOCVD apparatus for forming a high dielectric thin film, comprising asource ampule containing reactants in a solvent, a liquid micro-pump fordelivering the dissolved reactants, a vaporizer for vaporizing thedissolved reactants delivered by the micro-pump and a reactor fordepositing the vaporized reactants on a semiconductor substrate loadedtherein, said vaporized reactant being fed to said reactor by a carriergas, wherein said vaporizer is additionally provided with a solventsupply means for feeding an additional amount of the solvent to saidvaporizer, in order to prevent the reactants from being recondensed inthe vaporizer and the recondensed reactants, if may be present, fromblocking a transfer line between the vaporizer and the reactor.

In accordance with another aspect of the present invention, there isprovided an MOCVD method for forming a high dielectric thin film on asemiconductor substrate, comprising the steps of: feeding a reactantdissolved in a solvent to a vaporizer which is additionally providedwith the solvent via a separate supply means; vaporizing the reactant inthe vaporizer; and transferring the vaporized reactant to a reactor bycarrier gas, in which the reactant is deposited on the semiconductorsubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and aspects of the invention will become apparent from thefollowing description of embodiments with reference to the accompanyingdrawings in which:

FIG. 1 is a schematic view illustrating a conventional MOCVD apparatus;

FIG. 2 is a schematic view illustrating an MOCVD apparatus according tothe present invention; and

FIG. 3 is a graph in which the amounts of the residues according tosolvent amounts are plotted with respect to the temperature of thevaporizer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The application of the preferred embodiments of the present invention isbest understood with reference to the accompanying drawings.

Referring to FIG. 2, there is shown a concept for a MOCVD apparatusaccording to the present invention. As seen, the MOCVD apparatus of theinvention is identical to the conventional one in that it comprises asource ampule 10 containing reactants in a solvent, a liquid micro-pump20, a vaporizer 30 for vaporizing the liquid reactants, a reactor 70 fordepositing the reactants on a semiconductor substrate, a trap 60 forblocking injurious gas by cooling and a vacuum pump, different in thatthe vaporizer 30 is further equipped with a solvent supply means 100comprising a solvent ampule 40 and a pump 50.

A description will be given of the procedure for forming a highdielectric thin film, in connection with this figure.

As the reactants, Ba(DPM)₂, Sr(DPM)₂ and Ti(DPM)₂ (DPM stands fordi-pivaloyl methanate), or materials containing Sr, Ti and O₃ are used.These reactants are dissolved in a solvent in the source ampule 10 andtransferred to the vaporizer 30 by the liquid micro-pump 20. Isopropylamine is sufficiently fed to the vaporizer 30 by the solvent supplymeans 100, concurrently with the transfer, and vaporized along with thereactants. Isopropyl amine has an aim of preventing the recondensationof the reactants in the vaporizer 30 and in the transfer line betweenthe vaporizer 30 and the reactor 70. Thereafter, using carrier gas, suchas argon or nitrogen, the vaporized reactants are fed through thetransfer line to the reactor 70 and then, deposited on a semiconductorsubstrate loaded in the reactor to form a high dielectric thin film (forexample, BST or SrTiO₃ film)

As aforementioned, the recondensation of the reactants within thevaporizer 30 is attributed to the fact that the solvent is fastervaporized than the reactants although no heat is applied to thevaporizer because the solvent is lower than the reactants invaporization temperature.

Alternatively, each of the reactants, for example, Ba(DPM)₂, Sr(DPM)₂and Ti(DPM)₂, may be transferred to the vaporizer via individual sourceampules and liquid micro pumps.

According to another embodiment of the present invention, after thedeposition of the high dielectric thin film, sufficient solvent isre-fed to the vaporizer 30 via the solvent supply means 100 to removerecondensed reactant residues within the vaporizer, in order to preventrecondensed reactant residues from blocking the transfer line betweenthe vaporizer 30 and the reactor 70. Still remaining reactant residuesmay be removed by purge gas, such as argon and nitrogen.

Referring to FIG. 3, there are plotted the amounts of the residuesaccording to solvent amounts with respect to the temperature of thevaporizer. As seen, the residue proportion (wt %) is different dependingon the ratio of Sr(DPM)₂, the reactant to isopropyl amine, the solvent,at a temperature range of 100-600° C. The more the solvent, the less thereactant residue. It was found that, when the ratio of the reactant tothe solvent ranges from 1:10 to 1:20, the residues were little present.

Even when the ratio of the solvent to the reactant is high, the ratio islowered while the liquid mix is transferred from the source ampule tothe vaporizer. However, the additional feeding of the solvent to thevaporizer as in the present invention can maintain a sufficient amountof solvent. Such little residues as in the present invention reflect thereduction of the recondensed reactant in amount, meaning that theblockage of the transfer line occurs less frequently.

As described hereinbefore, a sufficient amount of solvent can beadditionally fed to the vaporizer when a high dielectric thin film isformed by use of the MOCVD apparatus of the present invention.Therefore, the recondensation of the reactant attributable to thedecomposition of solvent within the vaporizer can be minimized, therebysolving the problem of blocking the transfer line.

In addition, after the deposition of a thin film on a semiconductorsubstrate, it is possible to completely remove the reactant residuesremaining within the vaporizer by dissolving the residues in the solventby virtue of the additional solvent supply means provided to thevaporizer. Therefore, the aggravation of the thin film in physicalproperties owing to the contamination of the vaporizer can be prevented,and the reproductivity of thin film can be obtained as the reactants arestably fed to the reactor.

It is further understood by those skilled in the art that the foregoingdescription is that of preferred embodiments of the disclosed MOCVDapparatus and that various changes and modifications may be made in theinvention without departing from the spirit and scope thereof.

What is claimed is:
 1. A metal organic chemical deposition apparatus forforming a high dielectric thin film, comprising a source ampulecontaining reactants in a solvent, a liquid micro-pump for deliveringthe dissolved reactants, a vaporizer for vaporizing the dissolvedreactants delivered by the micro-pump and a reactor for depositing thevaporized reactants on a semiconductor substrate loaded therein, saidvaporized reactant being fed to said reactor by a carrier gas, whereinsaid vaporizer is additionally provided with a solvent supply means forfeeding an additional amount of the solvent to said vaporizer, in orderto prevent the reactants from being recondensed in the vaporizer and therecondensed reactants from blocking a transfer line between thevaporizer and the reactor.
 2. A metal organic chemical depositionapparatus in accordance with claim 1, wherein said reactants compriseBa(di-pivaloyl methanate)₂, Sr(di-pivaloyl methanate)₂ andTi(di-pivaloyl methanate)₂.
 3. A metal organic chemical depositionapparatus in accordance with claim 1, wherein said additional solvent isisopropyl amine.
 4. A metal organic chemical deposition apparatus inaccordance with claim 1, wherein said solvent supply means comprises asolvent ampule and a pump.